Watlow Series 922 - Manual (Page 24)

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WATLOW Series 922 User's Manual How to Install and Wire, Chapter 4
How To Eliminate Noise
• Use "snubbers" ("QUENCHARC™") to filter out noise generated by devices
such as relays, relay contacts, solenoids, motors, etc. A snubber is a simple
filter device using a 0.1
µ
f, 600 volt, non-polarized capacitor in series with a
100
Ω
, 1/2 watt resistor. The device can be used on A.C. or D.C. circuits to
effectively dampen noise at its source.
• The general purpose Watlow snubber, described above, is 0804-0147-0000.
For other "QUENCHARC" sizes contact:
PAKTRON
P.O. Box 5439
Lynchburg, VA 24502
Phone: 804/239-6941
• A Metal Oxide Varistor (MOV) can be used to limit voltage "spikes" that occur
on the A.C. supply lines as a result of lightning strikes, switching large
motors, etc. The MOV is available in several varieties and for 115 or 230 volt
lines. The device dissipates the voltage "spikes" to ground and in doing so
repeatedly, deteriorates its ability to function. MOVs have a limited life.
• "Islatrols" and other similar power line filters are designed to carry the power
for the control circuit and "buffer" the control circuit from A.C. line noise.
Devices like the Islatrol use media (electromagnetic filtering) other than
electric circuits to filter out electrical noise. Take care in matching the power
capabilities of the filter with power demands of the circuit. Keep line filters as
close to the control as possible to minimize the area for interference pick up.
Noise Suppression Devices Available From Watlow
Watlow Winona stocks a few key noise suppression parts. You may order
these by calling your local Watlow distributor.
Item Electrical Ratings Part Number
Differential Mode Line Filter Refer to the Islatrol listing below.
Metal Oxide Varistor 150V, 80 Joule 0802-0273-0000
MOV 275V, 75 Joule 0802-0266-0000
Wiring Guide
Table 7 -
Noise Suppression
Device Ratings
How to Check for Ground Loops
To check for ground loops, disconnect the ground wire at the ground termina-
tion. Measure the resistance from the wire to the point where it was connected.
The ohmmeter should read a high ohm value. If you have a low ohm value
across this gap, there is at least one ground loop present in your system.
Also, check for continuity; your reading should be "open". If you do find conti-
nuity, you must now begin looking for the ground loops. Begin disconnecting
grounds in the system one at a time, checking for continuity after each discon-
nection. When continuity reads "open" you have eliminated the ground loop(s).
Also as you reconnect grounds, keep making the continuity test. It is possible
to reconnect a ground loop.